1. Field of the Invention
The present invention relates to electrical connectors with a latch for connecting circuit boards.
2. Description of the Related Art
Electrical connectors mounted on a mother board for receiving a daughter board thereby connecting these circuit boards are well known. The density of IC memories mounted in a single in-line memory module for a computer, etc. has increased so that it is frequent to mount IC memories on both sides of a circuit board. An electrical connector capable of receiving such a circuit board has been proposed. The plugging force for the circuit board that has 50 terminals or more is very large.
In order to increase the mount density, the thickness of circuit boards has been reduced so that there is the danger of warping of the boards under such large plugging forces. If there is any warping, the solder of IC memories can suffer microcracks. Accordingly, there is a demand for an electrical connector which requires small plugging force.
In order to meet the demand, an electrical connector with a latch has been proposed. This connector has a housing with an elongated groove into which a circuit board is inserted obliquely and then turned clockwise to a predetermined angle for latch.
Japanese UM patent application Kokai No. 61-206278 and U.S. Pat. No. 4,960,386 disclose rotary ZIF connectors wherein opposed terminals are spaced such that the distance between the contact points before a circuit board is inserted obliquely is larger than the distance between the contact points in contact with the inserted board thereby minimizing the plugging forces.
In the rotary low-plugging force connectors, the circuit board is not brought into contact with the terminals during insertion but upon rotation made after the insertion. No consideration is made for wiping action by which the contact points are cleaned to thereby prevent poor contact.
In the above Japanese UM Patent application, the distance between terminals before insertion is set equal to or larger than the thickness of a circuit board to be inserted, and nowhere is there any suggestion about the wiping action.
In the U.S. Pat. No. 4,960,386, the connector has no board guides, and the terminals are exposed so that if the contacts are warped, a circuit board abuts on the terminals and deforms them. Accordingly, the distance between the terminals is set larger than the thickness of the circuit board, thus providing no wiping action.
In either case, the wiping action is eliminated in order to keep the plugging force low. As a result, dirt and dust accumulate on the terminals after a while, causing poor contact.
In addition, the large terminal distance makes the connector large, failing to meet the demand for a high density, low profile connector.